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Driver Development Kit (DDK) Developer's Guide
The Driver Development Kit (DDK) Developer's Guide is for developers who build device drivers for the QNX OS.
Human interface device (HID) DDK
HID library reference
hiddi.h
hidd_num_buttons()
Get maximum number of buttons returned in a report

Introduction
This introduction provides an overview of QNX Everywhere, how to get a QNX Software Development Platform license, and where to get support.
Self-Hosted Developer Desktop Guide
This guide provides instructions for building applications on QNX OS 8 using the self-hosted desktop, without the need for cross-compilation. It's built on the XFCE (XForms Common Environment) desktop environment, allowing QNX Everywhere users to start building QNX apps with minimal setup and friction.
Quick Start Target Image (QSTI)
This guide provides instructions on how to set up the Quick Start Target Image (QSTI) on a Raspberry Pi.
Custom Target Image (CTI)
This guide provides instructions on how to set up the Custom Target Image (CTI) on a Raspberry Pi.
Interfacing with your hardware
This chapter describes how to communicate with your given hardware.
The QNX Porting Guide
This guide provides comprehensive information on porting software from Linux to QNX.
Driver Development Kit (DDK) Developer's Guide
The Driver Development Kit (DDK) Developer's Guide is for developers who build device drivers for the QNX OS.
- Character I/O and UART (Universal Asynchronous Receiver Transmitter) DDK
- Inter-integrated circuit (I2C) DDK
- Serial peripheral interface (SPI) DDK
- Human interface device (HID) DDK
  - The HID architecture
  - Set up the driver skeleton
  - Connect to the HID server
  - Handle device events
  - Process device input reports
  - HID library reference
    - hiddi.h
      - Opaque structures
      - Function-like macros
      - Object-like macros
      - hidd_button_list_diff()
        Get the difference between two button usage lists
      - hidd_button_list_same()
        Get button usages common to two button usage lists
      - hidd_button_t
        HID button
      - hidd_collection_usage()
        Get a collections usage
      - hidd_connect()
        Connect to HID stack
      - hidd_connect_parm_t
        HID stack connection parameters
      - hidd_device_ident_t
        HID device identification
      - hidd_device_instance_t
        HID event callback functions
      - hidd_device_lookup()
        Find a device in connection’s reports
      - hidd_device_lookup_instance()
        Find device in connection’s device list
      - hidd_device_reset()
        Reset a device
      - hidd_disconnect()
        Disconnect a client driver from the HID stack
      - hidd_funcs_t
        HID event callback functions
      - hidd_get_all_buttons()
        Get all buttons that are currently activated
      - hidd_get_buttons()
        Get buttons that are currently activated
      - hidd_get_collections()
        Find device collections or sub-collections
      - hidd_get_idle()
        Get idle rate of a HID device
      - hidd_get_indexed_string()
        Get the indexed string
      - hidd_get_interface_string()
        Get the interface string
      - hidd_get_manufacturer_string()
        Get the manufacturer string
      - hidd_get_num_props()
        Get the number of properties in the report instance
      - hidd_get_product_string()
        Get the product string
      - hidd_get_protocol()
        Get the device protocol
      - hidd_get_report()
        Get an output or feature report from a HID device
      - hidd_get_report_instance()
        Get a report instance
      - hidd_get_report_props()
        Get the properties from the report instance
      - hidd_get_scaled_usage_value()
        Get scaled value from report for usage page and usage
      - hidd_get_serial_number_string()
        Get the serial number string
      - hidd_get_usage_value()
        Get value from report for usage page and usage
      - hidd_num_buttons()
        Get maximum number of buttons returned in a report
      - hidd_report_attach()
        Attach to a HID device report
      - hidd_report_collection()
        Get the collection from a report instance
      - hidd_report_desc()
        Get a report from device instance handle
      - hidd_report_detach()
        Detach from a HID device report
      - hidd_report_extra()
        Get a pointer to the memory allocated by the extra parameter
      - hidd_report_len()
        Get length of a raw report sent/received by device
      - hidd_report_props_t
        HID report properties
      - hidd_reports_detach()
        Detach from all the HID device reports for a device
      - hidd_send_report()
        Detach from all the HID device reports for a device
      - hidd_server_info()
        Get the connected HID server and DDK versions
      - hidd_server_info_t
        HID server and DDK version
      - hidd_set_buttons()
        Set buttons in a report
      - hidd_set_idle()
        Set idle rate of a HID device
      - hidd_set_protocol()
        Set device protocol
      - hidd_set_usage_value()
        Set value in report
    - hidut.h
  - HID input demo
  - HID stub driver
- Touch DDK

hidd_num_buttons()

Get maximum number of buttons returned in a report

Synopsis:

#include <sys/hiddi.h>

int hidd_num_buttons( struct hidd_report_instance *report_instance,
                      _Uint16t *max_buttons );

Arguments:

report_instance: The handle of a report instance, as returned by hidd_get_report_instance().
max_buttons: A pointer to memory where to store the number of maximum number of buttons that will be returned in the report.

Description:

The hidd_num_buttons() function gets the number of buttons returned in a report. This function is typically used to get the buffer sizes that need to be allocated for use with hidd_get_buttons().

Returns:

EOK: Success.
EINVAL: The report or max_buttons is NULL.

Classification:

QNX OS


Safety:
Cancellation point	Yes
Signal handler	No
Thread	Yes

Page updated: January 08, 2026